Mostly all Yautja wore armor for protection during hunts & missions when battling against prey, but most predators wore armor plates covering their knee, shoulder, hip, chest, thigh & other certain parts of the body(etc).

The material of the armor is unknown, But the more advanced type worn by the Spear Masters were made out of Pheonix that could withstand the acid blood of the Xenomorph.

It is unknown why most Yautja don't wear a full set of body armor, Celtic on the other hand is the only one at this time who wore a fully set of body armor which is shown on the film Aliens vs Predator.

This reason could be in fact that wearing a full set of armor would be less honorable & maybe only the young bloods would have the choice to have a full set of body armor.An example of a "normal" hunter's armor.